The present invention relates to a heat sink fin assembly (hereunder sometimes referred to merely as "fins" or "heat sink fins") for use as a heat sink of an LSI package. More particularly, the present invention relates to a heat sink fin assembly which is light-weight and can be mass-produced, and which can be used with a wide range of air-blowing angles to cool the LSI package.
In a typical LSI package, an IC chip is hermetically sealed to protect it from the environment. As the degree of integration of LSI's increases, the amount of heat generated by the LSI's also increases. Due to such an increased amount of heat, it is possible for a malfunction to occur and for the hermetic seal to be damaged resulting in serious problems. In order to avoid such problems, it is necessary to release heat from the IC chip to outside of the package. For this purpose LSI packages with heat sink fins have been employed.
FIG. 1 is a cross-sectional view of a ceramic LSI package 2 of the pin grid array type to which heat sink fins 3 are fixed.
The IC chip generally indicated by 1 is bonded onto a heat conducting plate 12 and is placed within an airtight space 14 that is defined by frame-like ceramic plates 9 and 10 and a metallic lid 13. The heat conducting plate 12 is bonded to ceramic plate 10, and lid 13 is bonded to ceramic plate 9 by a suitable method such as brazing, and the mating surfaces of the ceramic plates 9 and 10 are sealed together by means of a glass layer. The IC chip is electrically connected to pins 11 inserted into the ceramic plate 9 via lead wires 7 and the conductive circuit (not shown) drawn on the surface 10a of the ceramic plate 10.
The material forming the heat conducting plate 12 must have a high heat conductivity but a small difference in thermal linear expansion coefficient from the IC chip 1. Usually copper-impregnated tungsten is used.
Heat generated by the IC chip 1 is transmitted through the heat conducting plate 12 into heat dissipating fins 3, from which the heat escapes to the outside via air blown onto the fins.
The heat sink fins 3 are made of pure aluminum or aluminum alloys which have a high degree of heat conductivity, and in addition are light-weight and economical. Heat sink fins of various shapes have heretofore been proposed. As typical examples of the heat sink fins, a channel-type heat sink and pin-type heat sink will be described.
FIGS. 2a and 2b show an example of a channel-type heat sink fins 8, i.e., channel fin device, in which FIG. 2a is a plan view thereof and FIG. 2b is a front view. The channel fin device 8 comprises a plurality of heat dissipating plates 8a arranged parallel to one another and vertically extending from a rectangular base 8b. The channel fin device 8 is manufactured by plastic deformation such as hot extrusion, or by machining.
FIG. 3 shows how to carry out the hot extrusion. A heated billet 16 is inserted in the container 25 and is pressed with a plunger 17 so that a long semifinished product 19 is extruded through a hole 20 of a die 18 that is of the same shape as that shown in FIG. 2b. The semifinished product is cut into pieces of a length W.sub.2 to provide a channel fin device 8.
When producing the channel fin device 8 of FIG. 2a by machining, milling is adopted. FIG. 4 illustrates how milling is performed. A predetermined number of milling cutters 21 are rotated over a workpiece 22 (a material block of the same outside dimensions as the channel fin 8 to be produced) to cut grooves 23, which are made progressively deeper by continuing the revolution of milling cutters 21 until the channel fin device of FIG. 2a is obtained.
FIGS. 5a, 5b and 5c show an example of a pin-type heat sink fin 15, i.e., pin fin device, in which FIG. 5a is a plan view thereof, FIG. 5b is a side view, and FIG. 5c is a front view. The pin fin device 15 comprises a plurality of heat dissipating, rod-shaped pins 15a vertically extending from a rectangular base 15b. The pin fin device 15 is manufactured by plastic deformation, or by machining.
Japanese Unexamined Laid-Open Specification No. 12370/1976 discloses a method of producing pin fin device 15 via plastic deformation, such as cold forging. In this case, pure aluminum is used as a starting material, since pure aluminum exhibits good ductility at room temperatures.
FIGS. 6a and 6b illustrate how to carry out cold forging to produce the pin fin device 15 of FIG. 5a. In FIG. 6a shows that a material block 31 is set within a cavity 32b of forging die 32 with the block being confined by the surroundings. The dimensions of the cavity 32b are the same as those of the pin fin base plate, i.e., W1.times.W2. The forging die 32 has die holes 32a arranged with a predetermined pitch, and the die hole has an inner diameter corresponding to the diameter of the heat dissipating pin 15a. Within each of the die holes 32a, a knock-out pin 33 is provided at a predetermined depth. Forging is started by lowering a punch 34 to extrude the material block so that the thickness of the material block 31 is reduced and simultaneously the die hole 32a is filled with the material of the block 31. A plate-like portion 35b remaining on the die forms the base plate 15b for the heat dissipating pins 15a and the material 35a extruded into the die hole forms the heat dissipating pins 15a. After pulling up the punch 34, the knock-out pins 33 push up a forged product.
FIGS. 7a and 7b illustrates how milling, an example of machining, is performed. A predetermined number of milling cutters 21 of the disc type are rotated over a material block 22 to cut grooves 23 in one direction, and then as shown in FIG. 7b, another number of milling cutters 21' of the disc type are rotated to cut grooves 23' in the direction perpendicular to the direction of grooves 23. Cutting grooves 23, 23' is continued alternately and progressively to a depth until a pin fin device as shown in FIG. 5a is formed.